Cooling structures through use of a latent heat storage material storing heat by means of heat absorption associated with a phase change of a material have been conventionally known.
For example, Japanese Patent Laying-Open No. 2006-240501 (Patent Document 1) describes, in a cooling system for a hybrid vehicle, mixing, into a cooling medium, particles containing a latent heat storage material which undergoes a phase change at a cooling target temperature of a motor and an inverter and particles containing a latent heat storage material which undergoes a phase change at a cooling target temperature of an internal combustion engine system including the engine.
Japanese Patent Laying-Open No. 2000-116505 (Patent Document 2) describes applying a latent heat storage material to cooling of a heat-generating element of a cooker.
Japanese Patent Laying-Open No. 6-11286 (Patent Document 3) describes absorbing heat of an inverter by a heat storage material and applying the heat to space heating.
Japanese Patent Laying-Open No. 9-223576 (Patent Document 4) describes absorbing heat generated by a main circuit of a rice cooker by a heat storage material contained in a radiating fin.
Japanese Patent Laying-Open No. 61-7378 (Patent Document 5) describes specific examples of latent heat storage materials.
In a cooling structure with a semiconductor element mounted on a heat sink, cooling under normal conditions is performed by the heat sink. However, the amount of heat generated by the semiconductor element may be increased abruptly in a short time. An attempt to absorb this large amount of heat merely through use of the heat sink would cause the heat sink to have increased volume and increased heat resistance, thus raising the problem of degraded cooling performance under normal conditions. Accordingly, there is a demand for a structure that can absorb generated heat increased in a short time while preventing an increase in volume of the heat sink.
The latent heat storage material mainly utilizes heat absorption associated with a phase change of a material. For example, after the heat storage material in the solid phase melts into the liquid phase, the heat storage material cannot achieve heat absorption by latent heat until returned to the solid phase again. Therefore, the latent heat storage material is less likely to be suitable for cooling under normal conditions than the heat sink.
None of Patent Documents 1 to 5 discloses a structure with which the above problem can be sufficiently overcome. For example, Patent Document 1 merely describes mixing the latent heat storage materials into the cooling medium, but fails to describe providing separately a portion absorbing heat generated under normal conditions and a portion absorbing heat generated abruptly in a short time.